Chapter 3: Cell Membrane Flashcards
What forms bilayers in water due to their amphipathic properties?
Phospholipids
How do phospholipid molecules move within their monolayers?
By diffusion
What effect does increased saturation of phospholipid tails have on membrane fluidity?
Decreases fluidity
What happens to membrane fluidity as phospholipid tail length increases?
Decreases fluidity
How does temperature affect membrane fluidity?
Decreasing temperature reduces fluidity
What is the role of cholesterol in the cell membrane?
Mitigates changes in fluidity
What is the approximate thickness of the cell membrane?
7 nm
Which part of cholesterol is hydrophobic?
Tails
Which part of cholesterol is hydrophilic?
Heads
What type of molecule is cholesterol in terms of polarity?
Amphipathic
What is the function of cholesterol in animal cell membranes?
Provides mechanical stability
What is the primary composition of the cell membrane bilayer?
Phospholipids
How does the fluidity of the membrane compare to a mosaic?
Proteins and lipids move like icebergs in the sea
What does the term ‘mosaic’ in the fluid mosaic model refer to?
The scattered protein molecules
What are the two states that phospholipid tails can exhibit?
Saturated or unsaturated
What are intrinsic proteins?
Proteins embedded in the membrane
integral proteins
What are extrinsic proteins?
Proteins bound to intrinsic proteins or phospholipids
peripheral proteinsTis
Where are transmembrane proteins located?
Spanning the whole membrane
What role do glycolipids play in the cell membrane?
Cell signaling
What are glycolipids composed of?
Lipids with short carbohydrate chains
What is one function of glycoproteins?
Cell adhesion
Name two types of membrane proteins.
Intrinsic and extrinsic proteins
Which proteins provide hydrophilic pathways for ions?
Channel proteins
How do carrier proteins operate in facilitated diffusion?
By flipping between two conformations
Which process involves engulfing material into the cell?
Endocytosis
What is the bulk uptake of liquid by cells called?
Pinocytosis
What type of proteins allow charged substances to diffuse?
Channel proteins
What mechanism involves the release of materials from cells?
Exocytosis
What does it mean for the membrane to be semi-permeable?
Allows selective movement of substances
How do molecules move during diffusion?
Down a concentration gradient
What are factors that affects the rate of diffusion?
- Steepness of the concentration gradient
- Temperature
- Surface area
- Barrier thickness
- Distance
- Nature of molecules (size, polarity)
How does temperature impact diffusion?
Higher temperature increases diffusion rate
What types of molecules diffuse more slowly through the membrane?
Large
Why can water molecules diffuse rapidly despite being polar?
They are small enough
What is osmosis?
Movement of water from higher to lower water potential
Through what structure does osmosis occur?
Semi-permeable membrane
What is facilitated diffusion?
Diffusion through transport proteins
What provides energy for active transport?
ATP
What is an example of active transport in cells?
Sodium-potassium pump
What type of transport moves materials against a concentration gradient?
Active transport
Which process involves cell ‘eating’?
Phagocytosis
What is the key feature of a dilute solution in terms of water potential?
Higher water potential
What is required for bulk transport mechanisms?
Energy (ATP)
What happens to respiratory gases during diffusion?
They move across membranes
What is the main role of transport proteins in the membrane?
Facilitating the movement of specific molecules
What property allows phospholipids to form bilayers in water?
Amphipathic properties
How do unsaturated phospholipid tails affect membrane fluidity?
Increase fluidity
Why is the cell membrane referred to as ‘fluid’?
Because lipids and proteins can move around by diffusion
What does the steepness of a concentration gradient influence?
The rate of diffusion
Which type of transport requires energy input?
Active transport
How do large polar molecules like glucose move across the membrane?
Through transport proteins.
Glucose moves through its own channel called GLUT
What process allows respiratory gases like oxygen to cross membranes?
Simple diffusion
What type of transport involves moving materials into cells via vesicles?
Endocytosis
What is the main function of protein pumps during active transport?
To pump substances against the concentration gradient
How do channel proteins differ from carrier proteins?
Channel proteins provide fixed pathways; carriers change shape
What happens to plant cells in a dilute solution during osmosis?
Water enters the cell
What is the function of pinocytosis in cells?
Bulk uptake of liquids
What is a liposome?
A vesicle with phospholipid bilayer, can be used like a shipper to transport contents into desired location in body.
Why do saturated and long tails decrease fluidity of the membrane?
Makes membrane more compact, phospholipids are closer to each other
=> Strong LDF
=> Solidify
Why does decreasing temperature decrease membrane’s fluidity?
Lowers average kinetic energy
=> Phospholipids move slower and easier to solidify
Why are the hydrophobic tails important to the cell?
Prevents leakage and unwanted entrance of water-soluble substances.
How does cholesterol provides stability?
Stays between phospholipids
-> When high temp., prevents phopholipids to move around too much
-> When low temp., prevens phospholipids frmo packing together
What are the mechanism of phospholipid’s movements around the membrane?
- Lateral diffusion (side-side)
- Rotation around axis
- Flexion of tails (bend/flex)
- Transverse diffusion (turn around and change layer)
Why is the membrane fluid?
Phospholipids and proteins on it are always moving.
Tendency of molecules that can pass through membrane?
Small and non-polar
How many types of transport across membrane are there?
- Simple diffusion
- Osmosis
- Facilitated diffusion
- Active transport (includes bulk transport)
Mechanism behind simple diffusion?
Movement of substances down a concentration gradient.
How is water transport into and out of the cell?
Through membrane and channels called aquaporins
movement through aquaporins are more efficient
When a low C% solution is mixed with a high C% solution, does solute or solvent move?
Both.
Why does saline water contains exactly 0,9% NaCl?
Same concentration with cells and body fluids
=> Same osmotic pressure
=> No damage to cells
Mimics body’s electrolyte composition in extracellular fluids, same C% of Na+ and Cl-
What is hyper-/iso-/hypotonic?
Higher/same/lower concentration
Why do osmosis in plant cells differ frmo animal cells?
Plant cells have rigid cellulose walls
=> Isn’t strongly affected by osmotic pressure compared to animal cells
What happens when an animal cell is dropped into a hyper-/hypotonic solution?
- Hypertonic: crenation, water moves out of cell
=> Cell shrinks - Hypotonic: lysis, water moves into cell
=> Cell swells and bursts
What happens when an plant cell is dropped into a hyper-/hypotonic solution?
- Hypertonic: plasmolysed, lose water until protoplast shrinks away from wall
- Hypotonic: inflated until turgid
What are 2 types of transport proteins?
- Carrier proteins
- Channel proteins
Mechanism of channel proteins?
- Shaped like a gate:
1. Always open
2. Requires ATP to open (more common to control exchange)
Mechanism of carrier proteins?
- Flips between 2 shapes
- 2 types:
1. Open/close spontaneously (diffusion)
2. Requires energy to open/close (active transport)
